Deposition Of Bi Research Articles

On the influence of tin and bismuth UPD on Pt(111) and Pt(332) on the oxidation of CO

Deposition of Sn on a Pt(111) electrode gives rise to a sharp redox peak which is not due to the adsorption/desorption of Sn. The catalytic effect of this Sn-UPD on the oxidation of adsorbed CO is negligible. UPD of Sn on Pt(332) and Pt(755) on the other hand, has a remarkable catalytic effect; the onset of CO oxidation is shifted down to 0.25 V. Comparative experiments are presented for Bi deposition on these surfaces. Even when the bismuth coverage is high enough to block H-adsorption completely, CO is coadsorbed. Impedance measurements show that the rate of hydrogen adsorption is decreased by Sn UPD on Pt(111).

Potential Dependent Adhesion Forces on Bare and Underpotential Deposition Modified Electrode Surfaces

Adhesion force measurements are used to determine the potential dependence of the force of adhesion between a Si3N4 cantilever and a Au(111) surface modified by the underpotential deposition (upd) of Bi or Cu in acid solution or by oxide formation. The measured work of adhesion is near zero for most of the potential region examined in Bi upd but rises after the formation of a full Bi monolayer. The work of adhesion is high at positive potentials for Cu upd but then decreases as the Cu partial and full monolayers are formed. The work of adhesion is low in the oxide region on Au(111) but rises following the sulfate disordering transition at 1.1 V vs NHE. These results are interpreted in terms of the degree of solvent order on the electrode surface.

Electrooxidation of ethylene glycol on Pt-based catalysts dispersed in polyaniline

Platinum dispersed in a polyaniline film is a better catalyst than smooth Pt for ethylene glycol electrooxidation in perchloric acid aqueous solutions. The catalytic activity of the platinum microparticles is further enhanced when Ru, Sn or both are codeposited. The PAni/Pt–Sn assembly shows the highest electrocatalytic activity of the electrodes examined. Underpotential deposition of Tl and Bi on dispersed Pt inhibits EG electrooxidation while Pb causes significant catalysis only with a specific preparation method electrocatalyst. The morphology and the identity of the metallic dispersion is examined by transmission electron microscopy.

Photoemission measurements on clean and Bi-covered GaSb(111)A surfaces

Clean and bismuth-covered GaSb(111)A surfaces were characterized using low energy electron diffraction and synchrotron radiation photoelectron spectroscopy. The Ga 3d core-level spectra from the clean 2 × 2 reconstructed surface exhibit both bulk and surface components, while only one spin-orbit split component is required to fit the Sb 4d lines. The attenuation profile of the corelevel intensity with coverage indicates a Stranski-Krastanov growth mode for room temperature Bi deposition. The interface is apparently abrupt, but the overlayer is not epitaxially ordered. Line shape analysis of the Bi 5d, Sb 4d and Ga 3d core-level spectra shows that chemical bonding takes place primarily between the adsorbed Bi atoms and the Ga atoms of the substrate

Surface alloying and dealloying in [formula omitted] at low coverage

Using surface X-ray diffraction we have investigated the structure of the Bi Cu surface alloy formed after Bi deposition on Cu(001) at room temperature. At low Bi coverage below about 0.35 ML (1 ML = 1.53 × 10 15 atoms cm −2), the intensity distribution along the integer order crystal truncation rods indicates surface alloying where Bi atoms substitute Cu surface atoms. The Bi atoms adsorb 0.61 (10) Å above the surface Cu layer. At a coverage above about 0.35 ML where the formation of a well-ordered c(2 × 2) superstructure starts to set in, we observe surface dealloying indicated by a rapid decrease of the fractional Cu occupancy of the surface layer with increasing Bi coverage. The Bi atoms are located in hollow sites at an adsorption height of 2.27 (10) Å corresponding to a hard sphere radius of 1.63 (8) Å, somewhat below the metallic radius of 1.82 Å.

Strain relaxation induced 1-dimensional and 0-dimensional structures: Bi on Ge(001)

The growth of bismuth on Ge(001) has been studied using scanning tunneling microscopy. Deposition of one-monolayer (ML) Bi at room temperature and subsequent annealing at 500 K results in the formation of a well-ordered (2 × n) vacancy line network oriented perpendicular to the dimer rows. Deposition of two-monolayer Bi under the same conditions results in the formation of square-shaped pits with depths up to 10 ML. The edges of these pits run along the two dimer row directions. Careful analysis of these pits reveal that they mainly consist of (111) and (113) facets. We argue that the morphological transition from the vacancy line network to the square shaped pits pattern is driven by a modification of the surface strain tensor.

In situ REM observations of surfactant-mediated epitaxy: growth of Ge on Si(111) surfaces mediated by Bi

A study of growth of Ge on Si(111) surfaces mediated by Bi was carried out by reflection electron microscopy and reflection high-energy electron diffraction (REM-RHEED). A study of Bi-adsorbed Si(111) surfaces was also carried out. A “7 × 7” structure was formed by deposition of Bi below 200°C and it transformed into a (√3 × √3)- β structure at 200°C. Dark particles appeared on the surface at 200°C and the formation of the dark particles is the precursor of the formation of the (√3 × √3)- β structure. The (√3 × √3)- β structure transformed into a (√3 × √3)- α structure at 280°C and domain contrast was seen on the (√3 × √3)- α surface terraces. The density of three-dimensional (3D) islands of Ge on the Si(111)-Bi surfaces was higher and their size was smaller than those on the Si(111)(7 × 7) surfaces. Moreover, the critical thickness at which the layer growth of Ge transforms into the island growth on the surfaces with Bi was thinner than that on the bare surfaces. Smoothing of Ge films on the surfaces with Bi was observed.

LOCAL ORDER AT THE SURFACE OF BINARY ALLOYS IN RELATION TO THEIR CHEMICAL REACTIVITY

The behavior of binary alloys with respect to catalysis can be understood in terms of the geometric “ensemble effect” and/or the electronic “ligand effect.” For understanding, one has consequently to know precisely the local concentration and arrangement of both components at the very surface (in contact with the reactants), and also in the sublayers which influence electronically the outer atoms. Two kinds of well-defined surface are considered: binary alloys and well-controlled deposits of a given metal on a foreign metallic substrate. After a brief description of the driving forces for surface segregation and of metal-on-metal growth modes, the relations between surface composition/structure and reactivity of binary alloys are illustrated by some striking examples. In order to limit the discussion, the presentation is focused on platinum-based and palladium-based alloys. The ensemble effect is discussed first on the basis of the influence of inactive Bi, Pb or Sn deposits on Pt single crystal surfaces. For alloys, the PtCu3 (111), which exhibits a p (2×2) ordered surface structure in which the Pt surface atoms are all isolated by Cu atoms, offers a unique model sample for studying the dilution (of Pt by Cu) influence. The electronic influence of elements present in the sublayers is illustrated on PtNi (111) and Pt 3 Fe (111) samples, which present a quasicomplete Pt surface layer (with more or less Ni or Fe in the sublayers) and strong modifications of their chemisorptive properties and catalytic performances for some simple reactions. The properties of surfaces largely concentrated into Pd (either by large surface segregation in alloys containing low bulk Pd content, or by Pd deposition on various single crystal metal substrates) are discussed in the light of electronic modifications induced by the substrate atoms, with consequences on their chemical reactivity.

Sequential electrodeposition of silver and bismuth on a gold surface

AbstractSequential electrodeposition of Ag and Bi from a single electrolyte on Au (111) was studied by means of voltammetry and ion scattering spectroscopy (ISS). Silver was electrodeposited first under diffusion control. Subsequently, bismuth was deposited under potential sweep conditions. Underpotential deposition of BI on the gold surface modified with five Ag monolayers takes place similar to the deposition on the Ag (111) electrode. The deposited Bi can be electrodissolved completely with Ag remaining on the surface. However, the voltammetric characteristics of this process are different from the one in the case of Bi on the (111) surface of a silver single crystal. The ISS data suggest that this might be due to intermixing at the Ag/Bi interface occurring subsequent to the formation of the initial Bi on Ag structure on Au(111).

Step topography of Si(001) vicinals, clean and after deposition of As, Sb and Bi

We have used high-resolution LEED and AES on a spherically shaped sample to investigate the polar and azimuthal dependence of the step topography of Si(001) vicinals and its change by As, Sb and Bi adsorption. The well-established smooth transition on clean Si from single (S) to double (D) layer steps between 1.5° and 6° in the [110] azimuth is completely changed. After deposition at 300 K and equilibration by annealing at 970 ≤ T ≤ 1000 K the average step height for 0.75 ≤ θ As ≤ 1 ML becomes four layers (F) for all azimuths and miscut angles. No preferential orientation of the As adsorption dimers with respect to the F-step edges is observed. For Sb (720 ≤ T ≤ 770 K), θ Sb ≈ 1 ML and for Bi (600 ≤ T ≤ 750 K), S-steps are formed in all azimuths and for miscuts up to 10° from (001). These topography changes can be understood in terms of strain modifications induced by the adsorbates. Before complete desorption, both As and Sb induce c(4 × 4) patterns in all azimuths, connected with coverages of 0.25 ML. Also Bi induces a c(4 × 4) pattern but it is developed best at 920 K where Bi is already completely desorbed. Missing Si-dimer structures without adsorbate (Bi case) or with As or Sb filling the missing dimer sites are proposed.

Selective Oxidation of Cinnamyl Alcohol to Cinnamaldehyde with Air over Bi-Pt/Alumina Catalysts

The partial oxidation of cinnamyl alcohol to cinnamaldehyde with air in an aqueous solution has been studied over a series of Bi-Pt/alumina catalysts. The bimetallic catalysts were prepared by selective Bi deposition onto supported Pt particles of 3-4 nm. XPS and electrochemical measurements indicated that an increase in Bi/Pt s overall ratio results in higher Bi coverage and suppresses the hydrogen sorption on Pt, without any detectable influence on the electronic state of the noble metal. The bimetallic catalysts proved to be superior to 5 wt% Pt/alumina: an enhancement in initial rate by a factor of more than 26 was observed and the cinnamaldehyde yield increased by Bi promotion from 9 to 94-96% under otherwise identical conditions. Monitoring of catalyst potential during reaction, combined with cyclic voltammetric measurements, revealed that the low activity of Pt/alumina was due to the initial, destructive adsorption of the reactant ("self-poisoning"). The formation and irreversible adsorption of byproducts were suppressed but not eliminated by Bi promotion. Even the bimetallic catalysts were in a partially oxidized state when conversion exceeded 10-15%. There was no sign of "oxygen poisoning." On the contrary, a partial oxygen coverage of active sites enhanced the oxidative removal of surface impurities and accelerated the desired reaction. The main role of Bi promotion is a geometric (blocking) effect which decreases the size of Pt ensembles. In addition, at higher conversions Pi adatoms might behave as new active centers which adsorb OH better than Pt (bifunctional catalysis). The good selectivity (up to 98.5%) is due to (i) the negligible hydration of cinnamaldehyde, and to (ii) Pi promotion which decreases the catalyst potential during alcohol oxidation and hinders the further oxidation of cinnamaldehyde.

Geometry and electronic band structure of an ordered monolayer deposition of Bi on III-V(110) semiconductor surfaces.

We present calculational studies of the electronic and geometric structure of an ordered monolayer deposition of Bi on III-V(110) surfaces. The technique which we have applied to these systems relies on the complete self-consistent solution of the Kohn-Sham equations for both the electronic and ionic degrees of freedom. An ab initio pseudopotential method, within the local-density approximation, is used in a supercell approach. From a given initial set of atomic positions, a conjugate-gradient technique is used to achieve the equilibrium geometry by moving along the Born-Oppenheimer subspace. The calculated relaxed geometries of the clean and Bi-covered (110) surface of GaAs, InP, and InAs compare well with available low-energy electron-diffraction and x-ray standing-wave studies, and the electronic band structures agree with angle-resolved photoemission results. The orbital nature of states that might participate in Schottky-barrier formation at Bi-covered surfaces is also discussed.

SURFACE MORPHOLOGY ON Bi LAYERS IN MnBi MAGNETO-OPTICAL DISKS

Relations between surface roughness on the Bi layers and Bi deposition conditions on various substrates were investigated. On flat glass substrates, lower deposition rate and higher substrate temperature reduces the number of hillocks and surface roughness on Bi layers, and increases the degree of c-axis orientation. Bi layers on the grooved substrate with optimized deposition conditions have many large size hillocks (hundreds of nm order) at boundaries between lands and grooves. The two step deposition process for the Bi layer was newly developed to reduce the growth rate of hillocks. No hillock appears on the Bi layers at the land-groove boundaries when using this process. The noise reduction of 7 dB can be achieved by the two step deposition process for the Bi layer.

Fabrication of CuO 2-plane-based high-temperature superconducting thin films by atomic layer controlled molecular beam epitaxy

Bi 2Sr 2Ca n− 1Cu n O x (BSCCO) thin films and superconducting superlattices, (Bi 2Sr 2CaCu 2O x (2212)) l/ CuO y (2201)) m, have been fabricated by the atomic layer controlled molecular beam epitaxy (MBE) method using an oxygen radical beam. During the deposition, the surface structure has been investigated by reflection high energy electron diffraction (RHEED) observation. For the BSCCO crystal growth, in spite of the three-dimensional growth of Ca/Cu layers, recrystallization was caused by Bi deposition and surface flatness was improved. Consequently, the layered crystal structure was completed by the Bi deposition. This fact indicates a unit cell growth mechanism. It was also demonstrated that this atomic layer controlled MBE method has great advantages to control the number of CuO 2 planes in BSCCO and to fabricate the superconducting superlattices, (2212) l/(2201) m.

Partial charge transfer and adsorption at metal electrodes. The underpotential deposition of Hg(I), Tl(I), Bi(III) and Cu(II) on polycrystalline gold electrodes

The absorption of Hg 2+ 2, Tl +, Bi 3+ and Cu 2+ at polycrystalline gold electrodes from aqueous solutions is investigated by potentiostatic step experiments at rotating ring-disk electrodes. The macroscopic partial charge transfer coefficient l is determined from the initial part of the current transients at ring and disk which is diffusion controlled for low reactant concentrations. The measured l are 0.47 (Hg 2+ 2), 0.61 (Tl +), 0.73 (Bi 3+) and 0.92 (Cu 2+) ± 0.03. The potential dependence of the measured l is small and could indicate that the main part of l is caused by microscopic charge transfer λ. Diffusion controlled formation of the main part of the partially charged adsorbate points to strong repulsive forces between the adsorbed particles. With all of the investigated systems, a second type of deposit has been detected which consists of completely discharged metal.

Application of an Electrochemical Quartz Crystal Microbalance to a Study of the Anodic Deposition of PbO2 and Bi ‐ PbO2 Films on Gold Electrodes

The net rate of change in surface mass measured with respect to faradaic charge is calculated for electrodeposited films from the slopes of plots of frequency vs. charge . Abrupt changes in observed early in the deposition of and some films correspond to the transition from two‐dimensional island growth to one‐dimensional growth of the continuous films. Further, these changes in are a consequence of differences in the surface hydration of the deposited films in comparison with the substrate. XPS data indicate that Bi/Pb ratios in films correspond approximately to the [Bi3+]/[Pb2+] ratios in the deposition solutions. Further, voltammetric data for oxidation of dimethylsulfoxide indicate the catalytic activity of the films increases with the increased Bi/Pb ratios in these films. Nevertheless, limiting values of are virtually identical for the deposition of the films containing variable Bi/Pb ratios. The precision of the EQCM data does not allow designation of exact compositions of these various films. Nevertheless, we speculate that the EQCM data indicate the deposition of Bi3+ as Bi(V) with some Bi(IV), and the incorporation of in the films. Limiting values of for thick lead oxide films deposited in the absence of Bi3+ are within experimental error of the theoretical value of 1.24 mg C−1 for pure , and we conclude there is no evidence from the EQCM data for incorporation of and/or supporting electrolyte into these films.

Electrochemical Study of Autocatalytic Bismuth(III) Reduction with Ti(III)‐Complexes

It was first established that Bi(III) can be reduced by Ti(III) complexes in an autocatalytic mode and that the main features of the process can be interpreted in terms of pure electrochemical mechanisms. The electrochemical parameters of partial reaction coupling, which could be easily changed by means of the Bi(III) and Ti(III) ions complexation, govern the possibility of the process as well as its rate and the nature of the product formed (continuous film or stable sol). For the process to proceed it is necessary that not only the thermodynamic condition be met, but that the kinetic hindrances for the reductant oxidation be eliminated and these are realized when electroactive protonated Ti(III) complexonates are formed. The rate of Bi deposition onto the conductive surface in the acid medium is controlled by the partial reaction mixed current and is independent of , while the solution stability depends mainly on the and is independent of .

Initial growth mechanism of BiSrCaCuO thin films on SrTiO 3(110) surfaces studied by in-situ reflection high energy electron diffraction observation

The initial growth mechanism of Bi 2Sr 2Ca n−1 Cu n O x (BSCCO) films was investigated on SrTiO 3(110) surfaces by in-situ reflection high energy electron diffraction (RHEED) observation. The orientations in the BSCCO thin films were controlled by the flux of metal elements in the initial growth stage. A preceding deposition of Bi produced a RHEED pattern indicating the formation of a bismuth oxide layer which assisted the growth of a half-unit cell at the beginning of codeposition. A ( Bi: Sr: Ca: Cu =) 2:2:1:2 phase (117) orientation mixed with a c axis orientation was obtained. A preceding deposition of Sr, Ca and Cu produced a pattern indicating the formation of (Sr 1− x Ca x ) 2CuO 3 and caused epitaxial growth just after the start of codeposition, based on the structural relationship between the substrate and the perovskite structure part of the films. A 2:2:1:2 phase (119) orientation was formed.

Methanol oxidation on modified iridium electrodes

The electro-oxidation of methanol was studied in both acid and alkaline media, on clean iridium and on iridium electrodes modified by underpotential deposition and/or submonolayer deposits of Cu, Ag, Bi, Cd, Hg, Tl, Re and Pb. The catalytic effects of these atoms for methanol oxidation in acid medium decrease in the sequence Pb ≈ Bi > Tl > Cd > Cu > Hg. In alkali, with bare iridium the oxidation charges are 16 times larger than in acid, but the metal adatoms act as inhibitors. The results obtained in this work indicate that a favorable interaction among the adatom and the organic residue on the electrode surface probably exists. This interaction depends on the nature of the deposited metal.

Improved barrier layer for high-Tc superconductor on silicon

Buffer layer configurations consisting of magnetron sputtered ZrO2, Zr–Si mixed oxide, and SiO2 were investigated for sputter deposition of Bi–Sr–Ca–Cu–O high‐Tc superconducting thin films onto silicon wafers. A problem associated with film flaking during postdeposition annealing was overcome by burying the sample in a powder of Bi–Sr–Ca–Cu–O material. Crack growth and buckling in the buffer layers, associated with differential thermal expansions, were eliminated by raising the deposition temperature for the buffer layers. Unfortunately, the improved buffer layers were not good enough to prevent substrate–film interactions over the long annealing times (e.g., 14 h), and the sufficiently high temperature (e.g., 850 °C) needed for the formation of the 2223 high Tc (110 K) phase.